Switch-stacks: A scheme for microtasking nested parallel loops

The authors discuss run-time microtasking support for executing nested parallel loops on a shared-memory multiprocessor system, and present a scheme called switch-stacks for implementing such support. They first discuss current approaches to flat microtasking, and investigate how to extend these to full microtasking. They point out the problem of dummy waiting in the processor that initiates a parallel loop. To solve this problem, two schemes, dequeue-tasks and dequeue-descendant-tasks, are considered, and their disadvantages are discussed. The proposed switch-stack scheme perfectly solves the problem. These schemes have been implemented in the PARCEL run-time system. The results show that the new scheme nearly always achieves the best performance in execution time and stability